The following investigation of axons isolated as myelin-free entities via the myelinated axon and the axonal plasma membrane (axolemma) also obtained by fractionation of a purified preparation of myelinated axons is proposed. An isolation method devised for bovine white matter will be applied to obtain myelin, axolemma and myelin-free axons from human CNS white matter. The complete lipid and protein composition of these fractions will be determined. Lipid and protein analysis will also be analogous fractions isolated from rat and bovine CNS white matter. The lipid analysis will include the fatty acid composition of both sphingolipids and phospholipids. The turnover of sulfatide in axolemma myelin and myelin-free axons will be studied by intracerebral injection of radioactive sulfate into rat brains followed by sacrifice after appropriate intervals and preparation of the CNS cell fractions. Chase experiments with cold or unlabelled sulfate given some time after intracerebral injection of radioactive sulfate will be used to investigate possible precursor product relationships in the various fractions.